Climate change affecting North American forests, researchers find

Climate change is making North American forests more vulnerable to insects and disease but is helping some trees grow faster and increase their resistance to pests, a team of researchers from Dartmouth University said Monday.

Researchers reviewed almost 500 scientific studies dating to the 1950s to produce what they called the most comprehensive review of the affect of climate change on the forests that cover about one-third of North America. The effort was undertaken as part of the National Climate Assessment in 2012.

The researchers said that higher temperatures and increased carbon dioxide in the atmosphere are boosting tree growth, which could have a positive impact on economies that depend on timber and wood pulp, and could help pull carbon out of the ecosystem.

“We need to also start focusing on what could be — I don’t want to say ‘benefits,’ but the opportunities here,” said Aaron Weed, a Dartmouth postdoctoral researcher in ecology.

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Researchers found 27 insects and 22 diseases that are “notable agents of disturbance” in North American forests, according to their paper, published in the journal Ecological Monographs. Some areas devastated by insects or disease may be restored because of continued warming, with insects dying off because temperatures are too high for them, Weed said.

But warming also allows insects to flourish and exaggerates their natural role in keeping forests healthy, the researchers found. Various types of bark beetles, for example, are doing more damage than expected, they said.

“It is now clear that the large extent and expanding distribution of recent outbreaks have been permitted or exacerbated by increasing temperatures during the last decades,” the paper said. “Mountain and southern pine beetles are attacking hosts farther north and at higher elevations than historic norms,” in part because warmer winters are allowing insects to survive.

In addition to insects and disease, droughts and fires also have been linked to climate change, Weed said.